The development of self contained underwater breathing apparatus (“scuba”) has revolutionised underwater diving for both recreational and professional divers. The simplicity and reliability of modern scuba gear has extended the range and scope of diving activities to a much broader spectrum of society than originally envisaged when the prototype was first successfully tested in 1943.
The range of available diving activities extends from simple recreational pursuits through to specialised activities such as cave, ice and wreck doing. In warmer waters and particularly in tropical and subtropical areas near coral reefs, there is a great demand for diving tuition and diving expeditions. Many people, including the inexperienced, seek the experience of general and introductory diving activities.
In order to be a suitable candidate for undertaking scuba diving, it is necessary to have at least reasonable health with no major relevant disease conditions. Perhaps the commonest obstacle to scuba diving is asthma, which is both a pervasive disease in society and an exclusionary condition when considering diving. The incidence of asthma has been estimated variously at 10% in Australia and New Zealand, 4-7% in the USA and 6-8% in the United Kingdom. Even mild signs of the disease may be sufficient to bar participation in scuba diving, as the obstructive effect of this condition can be very marked. It has been noted that asthma increases the risk of lung barotrauma and represents a contraindication to diving (Heritier and Russi, Journal Suisse de Medicine 123(5):161-165, 1993). This blanket exclusion has been questioned. A suggested approach of bronchodilator inhalation prior to diving has been given some consideration (Coetmeur et al., Revue des Maladies Respiratoires 18:381-386, 2001). But without any controlled studies, this approach runs the risk of inappropriate medication or, perhaps more significantly, medication at a time removed from the trigger event and onset of bronchoconstriction, thereby proving ineffectual.
Experienced diving instructors will relate many stories of otherwise seemingly perfectly healthy people being excluded from diving glasses and the rewards of a diving experience, even when those people are asymptomatic. One perceived risk for such a person participating in scuba diving is that a sudden onset of a severe attack at any depth, or even on the surface, could have catastrophic and even fatal consequences. As pressure increases by one atmosphere for every 10 meters of depth, even at a depth of 5 meters, a diver must accommodate a 50% increase in ambient pressure. Respiratory embarrassment, even at this relatively shallow depth, may have significant adverse consequences. One of the unpredictable aspects of asthma is that the severity of episodes of dyspnoea is highly variable and also unpredictable.
The problem is not confined to scuba diving and may also arise when a person is snorkelling. The onset of difficult breathing may arise on the surface or while diving below the water level. Similar problems may arise in people in other contexts when they are required to don respiratory apparatus. This situation may arise in occupations such as pilot or fire officer and in workers at risk of exposure to gas or hazardous chemicals.
Aerosol medications are extremely well known for effective therapeutic intervention in an asthma attack when a victim is in normal atmospheric conditions. However, to date, it has not been possible to provide access to such therapeutic agents under water in scuba diving or snorkelling or in gas masks used generally in industrial settings. Likewise, powder and liquid therapeutic agents may also be administered via the respiratory system.
It should be noted that while the following disclosure is directed primarily to scuba diving and snorkelling arrangements, it is possible to transfer the same device and method to a wider range of situations for use with pressurised or otherwise delivered or channelled respiratory air supplies. Also, the term drug is used in its widest sense to include agents that are both therapeutic and recreational and agents which may have a mechanical effect on the respiratory tract such as maintaining moisture content or providing a surfactant activity or similar. Further, reference to asthma is exemplary only and other respiratory diseases as well as other conditions treatable via the respiratory or gastrointestinal systems may also be suitable for application of the present invention. Indications for the invention may include diseases or physiological effects due to increases and decreases of ambient pressures such as nitrogen narcosis and C.N.S. effects due to increased partial pressure of compounds in inhaled gas where these conditions are treatable via the respiratory or gastrointestinal systems.
It would be advantageous to provide a means of delivering a drug to a patient in a pressurised or unpressurised air stream underwater or on or near the surface of a body of water or elsewhere.